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Lecture 6' Microbial Adaptations 1

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Title: Lecture 6' Microbial Adaptations 1


1
Lecture 6. Microbial Adaptations 1
  • Extremophilic micro-organisms
  • Adaptive stresses
  • Thermophiles
  • Macromolecular stability
  • Psychrophiles
  • Halophiles
  • Acidophiles

2
Extremophiles
3
Adaptive stresses
  • Thermophiles
  • Psychrophiles
  • Halophiles
  • Acidophiles
  • Alkalophiles
  • Barophiles
  • Radiophiles
  • Oligotrophy
  • Denaturation and chemical destruction of macro-
    and small molecules membrane hyperfluidity
  • Membrane hypofluidity Slow reaction kinetics
  • Hyperosmotic stress
  • Chemical stability membrane potentials
  • Proton pumping against a negative pH gradient
  • Unfavourable reaction equilibria reaction
    kinetics
  • Molecular damage
  • Nutrient deficiency and uptake affinity

4
Thermophiles to Hyperthermophiles
5
Thermophilic biotopes and organisms
Bacillus stearothermophilus Thermus
aquaticus Thermotoga spp. Sulfolobus spp.
Pyrococcus spp. Pyrodictium spp. Methanococcus
Terrestrial and deep sea hydrothermal systems
Methanococcus jannaschii
6
Hyperthermophiles in the Tree of Life
BACTERIA
ARCHAEA
EUKARYA
7
Living at high temperatures Problems and
Solutions
  • Proteins denature at high temperatures.
  • Many essential small molecules (e.g., ATP, NADH
    etc) are unstable at high temperatures.
  • Membranes become more fluid at high temperatures.
  • Reaction rates increase with temperature
    metabolic overrun?
  • Thermodynamic stability of proteins is increased.
  • Not known exactly metabolic channeling may be
    important.
  • Membrane lipid compositions change to reduce
    fluidity.
  • Enzyme conformational mobility and expression
    levels control metabolic rates

8
Comparative stability of b-glycosidases
9
Molecular mechanisms of protein stability
  • Proteins are stabilised by weak intramolecular
    interactions (h? lt H-bonds lt ionic bonds) and
    protein-solvent interactions.
  • Comparisons of 3D x-ray structures of homologous
    proteins from different thermal sources show
  • gt Intramolecular packing
  • lt External loops
  • More helix-forming aas
  • Stabilised helix dipoles
  • gt Proline residues
  • lt Asn residues
  • Salt bridge networks

Higher protein stability
10
Protein stability a balance between the net
free energy of the folded and denatured states
  • N ? D model
  • DG comprises enthalpy and entropy components
  • Maximum enthalpy from intramolecular bonds
  • Minimum entropy
  • Folded proteins have high entropy
  • Solvent entropy is minimised in folded state

DG Free energy of denaturation
Unfolded
Folded
11
Stabilising lipids and reducing membrane fluidity
  • Increase hydrophobic interactions between lipids
  • Reduced fatty acid branching
  • Increased fatty acid chain length
  • Cyclisation
  • Stabilise chemically sensitive ester bonds
  • Ether-linked lipids in Archaea only
  • Reduce lateral mobility of lipids
  • C40 monolayer lipids in Archaea only

12
Psychrophiles living at low temperatures
Arctic, Antarctic, deep Marine and alpine
regions
13
Organisms at low temperatures
  • Psychrophiles Topt, 15oC, Tmax lt 20oC, Tmin ,
    lt0oC
  • Psychrotolerants (psychrotrophs) Topt, 20oC,
    Tmax gt 20oC, Tmin , gt3oC
  • Very wide species diversity of Bacteria, Fungi,
    Algae
  • E.g., Planococcus, Staphylococcus, Nostoc,
    Actinomyetes
  • Limited diversity of Archaea
  • Methanogens, uncultured crenarchaeota

14
PsychrophilesProblems and Solutions
  • Low metabolic rates
  • Membrane rigidity
  • Protein flexibility
  • Cytoplasmic freezing
  • Grow slowly
  • Adapt membrane fluidity
  • gt Unsaturation
  • lt Chain length
  • gt Methyl branching
  • Increase conformational flexibility
  • Reduce intramolecular bonding
  • Accumulation of solutes (freeze prevention)
  • Ice-nucleating proteins (freeze control)

15
Extreme halophiles
  • Living at very high salt concentrations
  • Vertebrates lt 1.5M
  • Halobacteria 1.5 3M
  • Haloarchaea 3 5.2M

16
Examples of moderate and extreme halophiles
  • Bacteria
  • Microccus
  • Bacillus
  • Flavobacterium
  • Halomonas
  • Vibrio
  • Alteromonas
  • Pseudomonas
  • Eukaryotes
  • Artemia
  • Dunaliella
  • Archaea
  • Halobacterium
  • Halorubrum
  • Haloferax
  • Haloarcula
  • Halococcus

17
Extreme halophiles in the tree of life
18
Extreme halophilesProblems and Solutions
  • Osmoregulation
  • Protein stability
  • Archaea
  • Accumulation of intracellular salts (5M KCl)
  • Bacteria
  • Accumulation of low molecular weight solutes
    (osmolytes) with osmotic potential
  • Increases in acidic a.a.s

19
Osmolytes
  • Glycerol (algae, fungi)
  • Sugars, polyols and derivatives
  • Glycine betaine
  • a-amino acids (P, E)
  • Ectoine, Hydroxyectoine
  • Charged or hydroxylated compounds
  • which H-bond with water molecules

20
Protein stability in Halophiles
  • High ionic strength (salt concentration)
    denatures proteins
  • Dissociation of salt bridges
  • Removal of protein water shell
  • Halophilic proteins have increased surface
    charged amino acids
  • Stabilised by K salt networks
  • Increased water shell
  • Many halophilic proteins require molar KCl for
    stability

21
Acidophiles
  • Geothermal areas
  • Acid mine drainage

pH 0 3
2So 3 O2 2 H2O à 2 H2SO4
4 FeS2 15 O2 14 H2O à 4 Fe(OH)3 8 H2SO4
22
Acidophiles are phylogenetically diverse
  • Eukaryotes
  • Fungi (numerous)
  • Algae (Cyanidium)
  • Protozoa (flagellates, ciliates, amoebae)
  • Bacteria
  • Heterotrophs (Alicyclobacillus, Acidiphilium,
    Sulfobacillus)
  • Autotrophs (Acidithiobacillus)
  • Archaea
  • Numerous heterotrophs and autotrophs, many
    thermophilic (Thermoplasma, Sulfolobus,
    Acidianus, Metallosphaera)

23
Chemoautotrophic metabolism in acidophiles
  • Sulfolobus
  • Acidianus
  • Stygioglobus
  • Aquifex
  • Sulfobacillus
  • Aerobic sulphur oxidation (So ? SO4-2 O2 ?
    H2O)
  • Aerobic sulphide oxidation (S-2 ? SO4-2 O2 ?
    H2O)
  • Anaerobic hydrogen oxidation (H2 So ? H2S)
  • Aerobic hydrogen oxidation (H2 1/2O2 ? H2O)
  • Aerobic iron oxidation (FeII ? FeIII O2
    ? H2O)

24
AcidophilesProblems and Solutions
  • pH homeostasis
  • Molecular stability
  • Intracellular pH trans-membrane potentials
  • Internal pH is maintained at 5-7 by maintained
    by proton pumping high external proton drives
    chemiosmotic ATP synthesis
  • Acid stable proteins
  • Stabilised by increase in charged amino acids
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